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Notes Payable - Principal Amount, Unamortized Debt Discount, Net Carrying Amount of the Liability Component, and Carrying Amount of the Equity Component of the 4.00% Debentures (Detail) (USD $)
In Thousands, unless otherwise specified
Jan. 31, 2013
Jan. 31, 2012
Debt Instrument [Line Items]    
Notes Payable $ 218,546 $ 214,573
4.00% Debentures due 2031
   
Debt Instrument [Line Items]    
Long-term Debt, Gross 253,000 253,000
Debt Instrument, Unamortized Discount 34,454 39,776
Notes Payable 218,546 213,224
Carrying Amount of Equity Component $ 43,930 $ 43,930